This invention concerns a device for producing pressure pulses in an oil well fluid medium flowing downward through borehole casing in a design according to the definition of species of claim 1.
In equipment such as that illustrated in U.S. Pat. No. 3,958,217, contact gaskets, especially O-ring gaskets are provided in the overlap area between the main valve body and the supporting body in order to completely suppress leakage of oil well fluid between the main valve body and the supporting body. At the same time this also assures that there will be no pressure drop in the inside flow channel when the auxiliary valve is actuated to induce a pressure pulse generating movement of the main valve body and thus the outlet opening of the inside flow channel is sealed.
However, the contact gaskets cause the development of dead water zones in the overlap area where solid particles entrained by the oil well fluid are deposited. Such sedimentation can cause movement resistance on the main valve body after only a short period of time which ultimately results in complete blockage. With an increase in the movement resistance, displacement can occur in the form and height of the pressure pulses caused by the movements of the main valve body in the oil well fluid medium with the result that the signals are no longer recognizable or they cannot be recognized correctly.